MEMS devices frequently operate based upon reactions to applied forces, pressures, and loads. In many systems, the manner in which a membrane or structure is deformed or deflected is used as a sensing or actuating function. Such deformation includes expansion and contraction, longitudinal bending, transversal bending, and torsional bending. Specific structural deformation is required in some specialized devices. For example, in Coriolis-effect-based MEMS vibratory gyroscopes incorporating a vibrating-plate topology concept, translational motion of a proof mass in drive direction is relied upon to provide accurate sensing functions. Any motion of the proof mass that is not purely within the drive direction can affect the accuracy of the device.
In many devices which incorporate a proof mass, movement of the proof mass is detected using electrostatic forces induced by capacitive comb drives or parallel plates and applied to either the proof mass or the proof mass frame, depending upon the particular device design. Movement of the proof mass along the drive direction is then sensed or effected while the proof mass is supported by a mechanical support such as a beam.
In many applications, different types of inertial sensor are incorporated. For example, it is beneficial to incorporate both accelerometers which sense linear motion along acceleration vectors ax, ay, and az, along with gyroscopes which detect rotational motion by angular rate vectors Ωx, Ωy, and Ωz. Such devices are typically referred to as six degrees of freedom or “6-DoF” sensors. From a system point of view, it would be beneficial to incorporate accelerometers and gyroscopes on a single integrated semiconductor chip. Such integration, however, is problematic.
Specifically, gyroscopes designed using a micromechanical vibratory principle of operation are permanently driven. Accordingly, a high quality factor in resonance is needed. In order to achieve a high quality factor in known devices, a low residual pressure is needed in the encapsulated chamber in which the seismic mass is located. Accelerometers designed using a micromechanical vibratory principle of operation, however, require a high damping to provide short time-scale sensitivity. Consequently, known accelerometers require a low quality factor. In order to achieve a low quality factor in known devices, a high residual pressure is needed in the encapsulated chamber in which the seismic mass is located.
Because of the conflicting quality factors, integrated sensors with gyroscopes and accelerometers require complex processing. In one approach, a system-in-package (SiP) solution includes assembling two different encapsulated chambers with two different pressures for two different MEMS elements in a single package. As an alternative to the SiP approaches, system-on-chip (SoC) approaches have been used. Known SoC approaches, however, suffer from a variety of problems. Such problems include cross-sensitivity issues, and increased processing requirements.
Consequently, commercially available sensors typically do not provide for 6-DoF. The above identified issues are further compounded when a system also requires geomagnetic field sensors which provide angle vectors θx, θy, and θz (or a nine DoF or “9-DoF” sensor).
What is needed therefore is a system and method of forming a system that provides a 6-DoF sensor which is simple to manufacture. A system and method of forming a system that provides a 9-DoF sensor would be further beneficial. It would be beneficial if the system and method of forming a system could be accomplished using known MEMS manufacturing processes.